1. Field
The invention involves thermal detectors and imagers sensitive to infrared radiation, particularly in the 8 to 14 micron wavelength region of the electromagnetic spectrum.
2. Prior Art
Thermal detectors and imagers may be generally divided into two classes, those which are quantum detectors such as solid state photoconductors, diodes and transistors; and those which employ thermally sensitive materials such as ferroelectric and pyroelectric compounds. The former class includes the group III-V and group II-VI materials such Gallium Arsenide and Cadmium Mercury Telluride. The latter class includes such materials as Barium Titanate, Rochelle Salt and Tri-glycine sulfate. Each material has its characteristic Curie point, i.e., the transition temperature where the material changes from being ferroelectric to paraelectric. This is accompanied by a rapid decrease in the dielectric constant as the temperature reaches the Curie point. By selecting proper amounts of two related materials a solid solution of the two materials may be fabricated which has a room temperature Curie point. For instance, a solid solution made of 66% BaTiO.sub.3 and 34% SrTiO.sub.3 should have a Curie point of approximately 20 C, i.e., room temperature. With such a material very small changes in thermal energy can be detected as the material goes through the transition point, as manifested in large changes in electronic capacitance or large changes in the electric constant. These dramatic changes in values constitute an electronic signal. When this material is made into an array of very small detectors the resulting electronic signals from all the detectors form an electronic image of the thermal scene.
An important aspect of using Barium Strontium Titanate (BST) of this composition in such an array is the fact that unlike most thermal (IR) imaging systems, this system is uncooled; operating at room temperature by design. BST is, however, one of the most expensive and not necessarily the ideal material for this type of system. An object of the present invention is to provide an alternative material to BST operating in the same manner and utilizing similar characteristics in a thermal imaging system for operation at room temperature.